1. Field of Invention
The present invention is directed to an apparatus for stacking sheets of material that includes an accumulator and to a method for using the apparatus. More specifically, the present invention is directed to an apparatus for stacking sheets of material that includes an accumulator system with a rotary drive and to a method of using the apparatus.
2. Description of Related Art
Devices for stacking sheets of material, such as sheets of corrugated material, are well known. One example of a commercially available device is the AGS2000 Rotary Die Cut Stacker made by the assignee of the present invention, A.G. Stacker, Inc., Weyers Cave, Va. Further examples of such devices are disclosed in U.S. Pat. Nos. 3,321,202 to Martin and 3,419,266 to Martin, each of which is expressly incorporated by reference in its entirety.
FIGS. 1-4 illustrate a conventional apparatus for stacking corrugated blanks. As illustrated therein, a stacking machine 100 typically comprises a layboy section 102 which receives corrugated blanks, such as those produced by a rotary die cut machine 101, and discharges the corrugated blanks onto a transfer conveyor 104. The transfer conveyor 104 receives the blanks and transports them to a main conveyor 106. The main conveyor 106 has an intake end 108 and a discharge end 110. At its intake end 108, the main conveyor 106 is mounted to a base 112 at a pivot point 114 so that the conveyor may be pivoted to raise the discharge end 110 of the conveyor 106. At the discharge end 110 of the conveyor 106, an accumulator section 116 is controllable to selectively receive discharged blanks or to allow the discharged blanks to fall to the ground or another conveyor to form a stack.
In operation, the main conveyor 106 is pivoted about the pivot point 114 to lower the discharge end 110 of the conveyor to an initial position (the position illustrated in FIG. 2). Sheets of material (not illustrated) exit the die cutter 101 and are fed onto the main conveyor 106 at intake end 108, transported along the length of the main conveyor 106 to discharge end 110, and discharged from the main conveyor 106. As they are discharged, the sheets often strike a backstop 118 in the accumulator section 116 that stops the forward momentum of the sheets. The sheets settle down, typically onto a discharge conveyor (not illustrated), to form a stack of sheets (not illustrated). As additional sheets drop onto the top of the stack, the stack grows in height, and main conveyor 106 is pivoted to raise the discharge end 110 to a position higher than the top of the growing stack. FIG. 3 illustrates main conveyor 106 in the raised position.
Once a stack of sheets has reached a desired height, it is removed, and the process of forming an additional stack begins. However, to permit time to remove a finished stack without stopping main conveyor 106, accumulator section 116 is employed. Accumulator section 116 catches or accumulates a small stack of sheets as main conveyor 106 continues to operate so that the completed stack on the discharge conveyor can be removed. When the completed stack is removed, the main conveyor is returned to the lowered position illustrated in FIG. 2, the small stack on the accumulator is dropped onto the transfer conveyor, and additional sheets are added to the top of this new stack.
The accumulator section 116 includes a plurality of catcher elements 120. Catcher elements 120 include a first catching member 122 and a plurality of extending members 124. When the catcher elements 120 are activated, the first catching member 122 is rotated into the position shown in FIG. 2. The extending members 124 are moved from the retracted position shown in FIG. 2 into an extended position where they extend at least partially across the bottom of the accumulator section 116 to catch sheets exiting the main conveyor 106. After the stack below the accumulator section 116 has been removed, the extending members 124 are retracted to drop the partial stack being formed thereon onto a discharge conveyor.
Existing accumulator designs are complex and generally require considerable manufacturing labor. As illustrated in FIG. 4, a conventional accumulator includes an air cylinder 132 having a projecting rod 134 extending perpendicularly to the direction of travel of the main conveyor 106, which rod drives a bar 136. The bar 136 is connected to a gear rack 138 extending transversely across the width of the main conveyor 106. The gear rack 138 engages a plurality of horizontally disposed large pinion gears 140 on pinion shafts 142 which pinion shafts 142 also each support a small pinion gear 144 (the pinions and pinion shafts are enclosed in housings that are not shown). The small pinion gears 144, in turn, engage rack teeth 146 on the sides of the extending members 124 and cause the extending members to extend and retract when the small pinion gears 144 rotate.
The gear ratio between the diameter of the large pinion gears 140 and small pinion gears 144 is selected to allow the eight inch travel of a typical air cylinder rod 134 to move the extending members a distance of about 20 inches. With this arrangement, linear motion must be converted to rotary motion, the rotary motion must be amplified with a selected gear ratio, and the rotary motion must be reconverted to linear motion to operate the accumulator. This arrangement is not only relatively expensive to manufacture, but in addition, the air cylinder may limit the accuracy with which the extending members 124 can be positioned.
There have been other attempts to address the problem of sufficient velocity control and position control in conventional systems. For example, U.S. Pat. No. 6,042,108 to Morgan discloses a flexible curtain which is extended into the stream of sheets. The disclosed flexible curtain system is complex with many moving parts and increases both material and manufacturing costs. Accordingly, it would be desirable to provide an improved accumulator system for a sheet stacking device.